Comparison
Context Window vs Time to First Token
Context Window and Time to First Token are both common AI/LLM terms but cover different ideas. Here is a quick side-by-side.
When you would reach for Context Window
Context Window comes up when the question is fundamentally about inference.
GPT-4o: 128K context.
When you would reach for Time to First Token
Time to First Token comes up when the question is fundamentally about inference.
Claude with a 50K-token cached prefix: TTFT drops from ~6s to under 1s on subsequent calls reusing the same prefix.
Frequently asked
What is the difference between Context Window and Time to First Token?
Context Window: The context window is the maximum number of tokens an LLM can consider in a single call — prompt plus generated output combined. Time to First Token: Time to first token (TTFT) is how long it takes from sending a request until the first response token arrives. The user-perceived latency metric for streaming chat.
When should I use Context Window vs Time to First Token?
Context Window is the right concept when you are focused on inference. Time to First Token applies when you are focused on inference.
Are Context Window and Time to First Token the same thing?
No. Context Window is inference; Time to First Token is inference. They are related but address different parts of the AI stack.